1) Field of the Invention
The present invention relates to a copying machine, and more particularly to a copying machine having a fluorescent lamp as its document exposure light source.
2) Description of the Prior Art
Conventionally, an output of a fluorescent lamp of the noted type is subject to variations depending on the temperature of its lamp tube wall. Accordingly, the fluorescent lamp has the disadvantage in that it is impossible to constantly obtain a sufficient amount of light from the lamp until its tube wall is properly warmed up.
A prior-art invention disclosed in a Japanese laid open patent No. 61-102659 has suggested a copying machine in which its fluorescent lamp is turned ON upon input of a copy start command and a copy run is initiated after an output of a light amount sensor for detecting a light amount of the lamp has reached a predetermined value.
With the above copier; however, there remains a problem as follows. That is, since the fluorescent lamp is turned ON only after the input of a copy start command, the lamp needs to be repeatedly turned ON and OFF if a plurality of copy operations are to be carried out in succession. This means that the copier is incapable of service while raising the lamp tube wall temperature which has been reduced during the OFF state of the lamp. Consequently, it will take a longer time period for completing all the copy operations.
Another prior-art invention disclosed in a Japanese laid-open patent No. 61-275735 has suggested a copying machine in which its fluorescent lamp is turned ON after being preheated for a predetermined time period subsequent to an ON operation of a power switch and a copy operation is permitted when a light amount of the lamp has reached a predetermined value. Further, with this copying machine, the fluorescent lamp is turned ON for testing its current output light amount not only immediately after the power-ON but also during disillumination or standby illumination condition of the lamp after an exposure operation.
With this copying machine, the fluorescent lamp is turned OFF or is repeatedly placed under the standby illumination condition after each exposure operation. Therefore, if the lamp is turned OFF, the copier will suffer from the same disadvantege of an extended copying time period as described hereinbefore. On the other hand, if the lamp is placed under the standby illumination condition, there will arise new problems of power and life waste of the lamp if the successive copy operations occur at long intervals.